Summarizing values to Describe
What is biodiversity?
Biodiversity is basically the variety within and among life forms on a site,
ecosystem, or landscape. Biodiversity is defined and measured as an
attribute that has two components — richness
Richness = The number of groups of
genetically or functionally related individuals. In most vegetation surveys,
richness is expressed as the number of species and is usually called species
Evenness = Proportions of species or
functional groups present on a site. The more equal species are in
proportion to each other the greater the evenness of the site. A site with
low evenness indicates that a few species dominate the site.
Diversity can be use to describe variation
in several forms:
- Genetic (species, varieties, etc.)
- Life form (grasses, forb, trees, mosses, etc.)
- Functional group (deep rooted, nitrogen-fixing, soil crust, evergreen,
Why is biodiversity measured?
Biodiversity is a measure that combines richness and evenness across species.
It is often measured because high biodiversity is perceived a synonymous with
ecosystem health. In general diverse communities are believed to have
increased stability, increased productivity, and resistance to invasion and
Diverse habitats with a variety of plants can have benefits such as:
- Providing forage for a variety of insect and vertebrate species.
- Stability resulting from plants in the community that are able to
survive drought, insect plagues, and/or disease outbreaks so that the site
will have some soil protection/forage/etc. in those years.
- Plants containing a variety of genetic material that may be useful in
long-term survival and stability of the community.
- The community benefits from a mixture of plants:
• soils improve with nitrogen fixers, deep
rooted plants bring nutrients up from soil layers below other plants roots.
• some species work together so that both can
survive (called commensalism) and therefore, diverse communities can be more
- Healthy diverse plant communities generally have all niches filled and
are theoretically less likely to be invaded by noxious or opportunistic
Though seldom acknowledged, there are also disadvantages to high
- Diverse communities are often a sign of fragmented or somewhat degraded
sites where much of species richness is contributed by disturbance species.
- Plant communities with high diversity can be more difficult to manage
for grazing because different species of plants
have different grazing tolerances and different rates of phenological
- Many plant communities are very stable with few species that are well
adapted to the environment.
Biodiversity Can be Expressed at Several Scales
Biodiversity can be measured and monitored at several spatial scales.
Alpha Diversity = richness and
evenness of individuals within a habitat unit. For example in the figure below,
Alpha Diversity of Site A = 7 species, Site B = 5 species, Site C = 7
Beta Diversity = expression of diversity
between habitats. In the example below, the greatest Beta Diversity is
Site A and C with 10 species that differ between them and only 2 species in
Gamma Diversity = landscape diversity or
diversity of habitats within a landscape or region. In this example, the gamma
diversity is 3 habitats with 12 species total diversity.
Site A = 7 Species
Site B = 5 Species
Site C = 7 Species
A vs B = 8 species
B vs C = 4 species
A vs C = 10 species